In cable television systems and the like, services are distributed by a headend to multiple subscribers. A conventional television service distribution system is shown in FIG. 1. According to FIG. 1, television programming may be received at a headend from multiple sources including, but not limited to, satellites, over the air broadcast antennas, and locally originated transmissions generated such as local or regional programming such as a local all news channel and the like. Satellites may include, but are not restricted to, Hotbird 1, Eutelsat 11-F1, Astra 1C, Intelsat 707, Tele X, Thor, Sirius, Astra 1D, Intelsat 601, TV Sat 2, and Astra 1A. Services typically include premium channels such as HBO and Showtime, impulse pay-per-view (IPPV) channels, basic cable channels such as ESPN, CNN, and MTV, and other channels.
According to the system of FIG. 1, the headend 10 receives services from the communications satellites 15. The headend 10 receives channels from the satellites 15 transmitted in the frequency spectrum (e.g., L-band) allocated to such communications. The headend 10 can be configured to receive a multitude of channels up to its channel carrying capacity. A typical headend may be configured to broadcast 120 channels to its subscribers. Of the 120 channels, 100 may constitute services from satellites, 12 may be over-the-air channels, and eight may be local origination channels.
The satellites 15 generally broadcast more than 100 services. Consequently, the headend 10 selectively receives services from the broadcasting satellites 15. The channels received from the satellites 15 are scrambled by the service providers to prevent unauthorized interception of the services by unauthorized receivers. The service providers are the organizations that generate the channels and send put them on the satellites 15 for distribution by authorized headend operators. The techniques for scrambling the channels include, but are not restricted to, sync inversion, line inversion, sync suppression, and many others known in the art.
The headend 10 includes one video receiver 20 per channel received from the satellites 15. Each video receiver 20 tunes to an L-band frequency associated with the selected channel received from the satellites 15. Thus, each video receiver acts as a different satellite signal receiver. Each received channel undergoes the same process when received at the headend. The video receiver 20 downconverts the received scrambled channel to baseband. A decoder 25 decodes and descrambles the baseband scrambled channel to recover a baseband audio/video channel. The decoder may be a standard D-MAC decoder known in the art. Each individual decoder 25 descrambles one received channel, and the specific descrambling technique employed from one decoder to another depends on the scrambling method originally used by the service provider in broadcasting the channel to the satellite 15.
The headend 10 includes one or more device units 30 for handling the channels distributed. For example, in FIG. 1, four units 30 (group A, group B, group C, and group D) are shown. It should be understood that the number of units may vary depending on factors like the number of channels.
The group A unit 30 includes video modulators 35, a video modulator 45, and an agile upconverter 50. Each video modulator 35 is operatively coupled to a respective one of the decoders 25, and modulates a received baseband audio/video channel to a uniquely assigned RF channel. A combiner 55 combines the RF channels and outputs the same to the master combiner 60. It is to be understood that any number of devices may be located between each video decoder 25 and its corresponding video modulator 35 to perform one or manipulations/modifications to the baseband audio/video channel prior to distribution to the subscribers. For example, devices for scrambling the channels for subscriber distribution may be necessary to prevent subscribers who do not subscribe to a particular channel from receiving the channel without the proper descrambler. Also, character insertion and screen overlays devices may be utilized.
In the group A unit 30, video modulators 35 are serially coupled together by the dashed lines shown and connected to video modulator 45. The video modulator 45 and agile upconverter 50 together provide unit level backup or redundancy for the video modulators 35 of the group A unit 30. When one of the video modulators 35 is inoperable or otherwise fails, the baseband audio/video channel directed to the inoperable video modulator 35 is rerouted to the video modulator 45. Any video modulators 35, between the failing video modulator 35 and the video modulator 45, bypass the baseband audio/video channel of the failing video modulator 35 to the video modulator 45. The video modulator 45 converts the baseband audio/video channel to an intermediate frequency. Then, the agile upconverter 50 upconverts the signal to the appropriate RF channel and sends the RF channel to combiner 55. The combiner 55 combines the redundant RF channel with the other RF channels output by the operable video modulators 35 of the group A unit 30. The group A unit 30 outputs a combined RF signal including a plurality of channels to a master combiner 60.
The group B unit 30 receives baseband audio/video channels from decoders 25 connected thereto. Local origination channels 65 in the form of audio/video channels are distributed to the group B unit 30, group C unit 30, and group O unit 30. The local origination channels 65 can include audio and video channels received by the headend 10 from a local studio or otherwise for distribution to the subscribers.
The group B unit 30 processes the received channels in the same manner as the group A unit 30 and outputs an RF signal including each of the received channels to the master combiner 60. The group C unit 30 receives locally originated channels 65 in the form of audio/video channels and processes the received channels in the same manner as the group A and B units 30 and outputs an RF signal including each locally originated channel to the master combiner 60.
The group D unit 30 receives locally originated channels 65 in the form of audio/video channels. Each video modulator 35 in the group O unit 35 modulates a received audio/video channel to a uniquely assigned RF channel, and the RF channels are combined by a combiner 55. In the group D unit 30, video modulators 35 are serially coupled together by the dashed lines shown and connected to the video modulator 45. When one of the video modulators 35 is inoperable or otherwise fails, the video modulator 45 receives the audio/video channel originally destined for the inoperable video modulator 35 and modulates the channel to a first frequency (e.g., IF).
The headend 10 receives over-the-air (off-air) channels via antenna 70. An RF-IF downconverter 75 coupled to the antenna 70, downconverts the channels from RF to IF. The downconverter 75 forwards the IF channels to upconverters 85 in the group D unit 30. Each upconverter 85 receives an IF channel input from the downconverter 75 and upconverts the received channel to a unique RF channel.
The video modulator 45 of the group D unit 30 and the upconverters 85 are serially coupled to the agile upconverter 50 by the dashed lines shown. When the video modulator 45 outputs a frequency channel when one of the video modulators 35 is inoperable or otherwise fails, the agile upconverter 50 upconverts the first frequency channel to a redundant RF channel. In this instance, the upconverters 85 bypass the IF channel to the agile modulator 50.
Also, when one of the upconverters 85 is inoperable or otherwise fails, the IF channel input to the inoperable upconverter 85 is forwarded to the agile upconverter 50 which provides redundancy for the upconverters 85 and upconverts the IF channel to a redundant RF channel. The combiner 55 of the group D unit 30 combines the RF channel outputs of the video modulators 35, upconverters 85, and agile upconverter 50 and forwards the RF channel output signal to the master combiner 60.
A system manager 100 generates various control signals to control the operation of devices in the headend. An illustrative system manager may be the IH-2000 intelligent headend manager from Scientific-Atlanta, Inc. The system manager 100 produces video receiver control signals which instruct each of the video receivers 20 to tune to a unique channel received from the satellites 15. An expander 105 receives the video receiver control signals from the system manager 100 over an RS-232 connection. The expander 105 places the video control signals in the appropriate protocol and passes the control signals to the video receivers 20. The system manager 100 also monitors the operability of the video modulators 35 and upconverters 85 in the device units 30. When one of the video modulators 35 or upconverters 85 in a unit is inoperable or otherwise fails, the system manager 100 generates a control signal which redirects the input of the failing device to the redundant portion of the unit 30. As described above, when one of the video modulators 35 fails, the input to the inoperable video modulator 35 is redirected to video modulator 45 and agile upconverter 50. Similarly, when one of the upconverters 85 fails, a control signal redirects the input thereof to the agile upconverter 50 as previously explained. This control signal can be routed through an RS-232 connector to a NEXBUS RS-485 connector via a protocol converter 110 to the video modulators 35, 45, agile upconverters 50, and upconverters 85.
The failure of any device at the headend can result in the interruption of a service. This can be particularly troublesome during certain services. Disruption of IPPV services such as a boxing match or a movie can result in a loss of revenue. Thus, it is important to provide continuous service to maximize revenues and maintain customer satisfaction. The number of video modulators 35 per video modulator 45 and agile upconverter 50 combination in a device unit 30 is based on the desired redundancy, and is a design choice. The more video modulators 35 per video modulator 45 and agile upconverter 50 combination, the more likely that two video modulators 35 in the same unit 30 can fail, resulting in a service disruption.
The above system provides limited unit level redundancy to account for inoperability of the video modulators and upconverters in the units. However, the above system and more generally the prior art has failed to provide redundancy for other devices in the headend. Devices such as decoders and video receivers can break down resulting in revenue losing service disruptions. In addition, due to the increase in unauthorized receivers pirating satellite signals, satellite programming distributors have scrambled their signals to minimize loss in revenue. The existing unit level redundancy cannot provide backup for devices that process the scrambled signals. Thus, if one of those devices is inoperable and fails, then service will be disrupted. Accordingly, there is a need in the art for a system which can provide redundancy for devices in the power path from reception of the services to output of the RF channels to the subscribers including the video receivers and decoders.